Dedup data is not cleaned up in Consul KV storage

[bofm]

Consul Template version

v0.19.5 and master (fd266d9)

Expected behavior

Consul kv dedup storage should be maintained by Consul-Template. Stale /consul-template/dedup/<md5>/{data,lock} keys should be cleaned up automatically.

Actual behavior

Many unused old dedup data and lock keys are left in the Consul kv dedup storage.

What's strange is that /lock keys are not cleaned up by Consul's Session TTL mechanism when consul-template instances are shut down gracefully. But the /lock keys are cleaned up when consul-template instances are killed.
The /data keys are not cleaned up in any case.

Steps to reproduce

A script to run the testcase and it's output:

https://gist.github.com/bofm/677de0b543a071bab68bf77d070d6c3a

Run it in an empty directory on a host with consul and consul-template installed. It might be required to run several times to reproduce the problem.

Questions

Does consul-template really need two keys per template hash (both /data and /lock) for deduplication? I believe one key would be sufficient. Consul-template could acquire a session lock on /data key. To determine if the template is already rendered a custom flag on the key could be used.